Miror B. does have a Voltorb, deoxys and celebi master. You just gotta battle him in the Cave Pok? Spot. To meet him, you have to find Dunkin at the Rock Pok?spot. From there, it's pretty obvious. I forgot if he does have three Shadow Pok?mon total, but his final one is a freakin' Dragonite. (5 levels stronger than Lugia, too!)
Oh yeah, make sure you are playing Pok?mon XD: Gale of Darkness, not Pok?mon Colloseum!
And you can't get the Master Ball before battling Shadow Lugia for the first time. If you want to use the Master Ball on it, you have to defeat it. Then come back when Dr. Krane gives you the Master Ball.